DESCRIPTION: The acyl-CoA dehydrogenases (ACSs) are a family of evolutionarily related enzymes involved in the first step of beta-oxidation of fatty acids and in the intermediate metabolism of leucine, isoleucine, and valine. Deficiencies of these enzymes are increasingly being recognized as important causes of inherited defects of metabolism in humans. The long range objective of this application is to investigate important structure/function relationships in the ACD gene family at the molecular level. The general hypothesis is that this information will afford a better understanding of genotype/phenotype correlations in patients with deficiencies of these enzymes. Specific aims of this proposal include Aim I: molecular and functional analysis of IVD mutations in patients with isovaleric acidemia; Aim 2: analysis of the pathway of IVD maturation and assembly; and Aim 3: determination of substrate specificity within the ACD gene family. Mutant enzymes from patients with deficiencies of IVD will be studied at the molecular and biochemical level in order to correlate genotype with clinical phenotype. IVA cells with defects in IVD RNA splicing and stability, as well as gene transcription and mRNA translation will also be studied. Crystal structure of isovaleryl-CoA dehydrogenase will be used to direct site specific mutagenesis experiments to determine structural motifs and amino acid residues important in the formation of active enzyme tetramers. Finally, factors important in determining substrate specificity of the ACDs will be explored. Crystal structure of short chain acyl-CoA dehydrogenase (SCAD) and IVD will be used to guide construction of altered SCAD and IVD enzymes with enhanced ability to utilize octanoyl-CoA as substrate. These studies will lead to a more complete understanding of the ACD gene family, and an improvement in the ability to diagnose and treat patients with these disorders.